Image generation in an electronic device using ultrasonic transducers

ABSTRACT

A method for generating a composite image having an increased image pixel density by an array of ultrasonic transducers having a given spatial density is provided. The method comprises capturing a first set of pixels at an ultrasonic sensor using a first beamforming pattern, wherein the first beamforming pattern comprises a first pattern of ultrasonic transducers of the ultrasonic sensor. The method further comprises capturing a second set of pixels at the ultrasonic sensor using a second beamforming pattern, wherein the second beamforming pattern comprises a second pattern of ultrasonic transducers. The first beamforming pattern and the second beamforming pattern are different. Pixels of the second set of pixels correspond to positions between pixels of the first set of pixels. The method additionally comprises combining the first and second sets of pixels to form the composite image. An electronic device and a method of generating an image of a fingerprint are also provided.

BACKGROUND

Piezoelectric materials facilitate conversion between mechanical energy and electrical energy. Moreover, a piezoelectric material can generate an electrical signal when subjected to mechanical stress, and can vibrate when subjected to an electrical voltage. Piezoelectric materials are widely utilized in piezoelectric ultrasonic transducers to generate acoustic waves based on an actuation voltage applied to electrodes of the piezoelectric ultrasonic transducer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of the Description of Embodiments, illustrate various embodiments of the subject matter and, together with the Description of Embodiments, serve to explain principles of the subject matter discussed below. Unless specifically noted, the drawings referred to in this Brief Description of Drawings should be understood as not being drawn to scale. Herein, like items are labeled with like item numbers.

FIG. 1A is a diagram illustrating a piezoelectric micromachined ultrasonic transducer (PMUT) device having a center pinned membrane, according to some embodiments.

FIG. 1B is a diagram illustrating a PMUT device having an unpinned membrane, according to some embodiments.

FIG. 2 is a diagram illustrating an example of membrane movement during activation of a PMUT device having a center pinned membrane, according to some embodiments.

FIG. 3 is a top view of the PMUT device of FIG. 1A, according to some embodiments.

FIG. 4 is a simulated map illustrating maximum vertical displacement of the membrane of the PMUT device shown in FIGS. 1A-3, according to some embodiments.

FIG. 5 is a top view of an example PMUT device having a ring shape, according to some embodiments.

FIG. 6 is a top view of an example PMUT device having a hexagonal shape, according to some embodiments.

FIG. 7 illustrates an example array of circular-shaped PMUT devices, according to some embodiments.

FIG. 8 illustrates an example array of square-shaped PMUT devices, according to some embodiments.

FIG. 9 illustrates an example array of hexagonal-shaped PMUT devices, according to some embodiments.

FIG. 10 illustrates an example pair of PMUT devices in a PMUT array, with each PMUT having differing electrode patterning, according to some embodiments.

FIGS. 11A, 11B, 11C, and 11D illustrate alternative examples of interior support structures, according to various embodiments.

FIG. 12 illustrates a PMUT array used in an ultrasonic fingerprint sensing system, according to some embodiments.

FIG. 13 illustrates an integrated fingerprint sensor formed by wafer bonding a CMOS logic wafer and a microelectromechanical (MEMS) wafer defining PMUT devices, according to some embodiments.

FIG. 14 illustrates an example ultrasonic transducer system with phase delayed transmission, according to some embodiments.

FIG. 15 illustrates another example ultrasonic transducer system with phase delayed transmission, according to some embodiments.

FIG. 16 illustrates an example phase delay pattern for a 9×9 ultrasonic transducer block, according to some embodiments.

FIG. 17 illustrates another example phase delay pattern for a 9×9 ultrasonic transducer block, according to some embodiments.

FIG. 18 illustrates a plan view of simulated ultrasonic pressure on the focal plane for an example ultrasonic transducer system using three timing phases, according to an embodiment.

FIG. 19 illustrates a cross section of simulated ultrasonic pressure on the focal plane for an example ultrasonic transducer system using either three or five timing phases, according to an embodiment.

FIGS. 20A-C illustrate example transmitter blocks and receiver blocks for an array position in a two-dimensional array of ultrasonic transducers, according to some embodiments.

FIG. 21 illustrates an example ultrasonic transducer system with phase delayed transmission, according to some embodiments.

FIG. 22 illustrates an example ultrasonic transducer system with phase delayed transmission, according to some embodiments.

FIG. 23 illustrates an example ultrasonic transducer system with phase delayed transmission, according to some embodiments.

FIGS. 24A and 24B illustrate example phase delay patterns for a 5×5 ultrasonic transducer block, according to some embodiments.

FIGS. 25A and 25B illustrate another example phase delay pattern for a 5×5 ultrasonic transducer block, according to some embodiments.

FIG. 26 illustrates example simultaneous operation of transmitter blocks for a multiple array positions in a two-dimensional array of ultrasonic transducers, according to some embodiments.

FIG. 27 illustrates an example operational model of a transmit signal to a receive signal of a two-dimensional array of ultrasonic transducers, according to some embodiments.

FIG. 28 illustrates an example transmit path architecture of a two-dimensional array of ultrasonic transducers, according to some embodiments.

FIG. 29 illustrates an example receive path architecture of a two-dimensional array of ultrasonic transducers, according to some embodiments.

FIGS. 30A-30C illustrate using transmit beamforming to capture various image pixel densities, based on a two-dimensional array of PMUTs, in which in FIG. 30A, one image pixel is captured for each PMUT, in FIG. 30B, two image pixels are captured for each PMUT, and in FIG. 30C, four image pixels are captured for each PMUT.

FIGS. 31A-31B illustrate using transmit beamforming to capture various image pixel densities, based on an alternate two-dimensional array of PMUTs, in which in FIG. 31A, one image pixel is captured for each PMUT and in FIG. 31B, three image pixels are captured for each PMUT.

FIG. 32 is a flow chart is a flow chart illustrating one embodiment of a method for generating a composite image having an increased image pixel density in a given density of ultrasonic transducers.

DESCRIPTION OF EMBODIMENTS

The following Description of Embodiments is merely provided by way of example and not of limitation. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding background or in the following Description of Embodiments.

Reference will now be made in detail to various embodiments of the subject matter, examples of which are illustrated in the accompanying drawings. While various embodiments are discussed herein, it will be understood that they are not intended to limit to these embodiments. On the contrary, the presented embodiments are intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope the various embodiments as defined by the appended claims. Furthermore, in this Description of Embodiments, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present subject matter. However, embodiments may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the described embodiments.

Notation and Nomenclature

Some portions of the detailed descriptions which follow are presented in terms of procedures, logic blocks, processing and other symbolic representations of operations on data within an electrical device. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. In the present application, a procedure, logic block, process, or the like, is conceived to be one or more self-consistent procedures or instructions leading to a desired result. The procedures are those requiring physical manipulations of physical quantities. Usually, although not necessarily, these quantities take the form of acoustic (e.g., ultrasonic) signals capable of being transmitted and received by an electronic device and/or electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in an electrical device.

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the description of embodiments, discussions utilizing terms such as “capturing,” “combining,” “transmitting,” “receiving,” “sensing,” “generating,” “imaging,” or the like, refer to the actions and processes of an electronic device such as an electrical device.

Embodiments described herein may be discussed in the general context of processor-executable instructions residing on some form of non-transitory processor-readable medium, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or distributed as desired in various embodiments.

In the figures, a single block may be described as performing a function or functions; however, in actual practice, the function or functions performed by that block may be performed in a single component or across multiple components, and/or may be performed using hardware, using software, or using a combination of hardware and software. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, logic, circuits, and steps have been described generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. Also, the example systems described herein may include components other than those shown, including well-known components.

Various techniques described herein may be implemented in hardware, software, firmware, or any combination thereof, unless specifically described as being implemented in a specific manner. Any features described as modules or components may also be implemented together in an integrated logic device or separately as discrete but interoperable logic devices. If implemented in software, the techniques may be realized at least in part by a non-transitory processor-readable storage medium comprising instructions that, when executed, perform one or more of the methods described herein. The non-transitory processor-readable data storage medium may form part of a computer program product, which may include packaging materials.

The non-transitory processor-readable storage medium may comprise random access memory (RAM) such as synchronous dynamic random access memory (SDRAM), read only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, other known storage media, and the like. The techniques additionally, or alternatively, may be realized at least in part by a processor-readable communication medium that carries or communicates code in the form of instructions or data structures and that can be accessed, read, and/or executed by a computer or other processor.

Various embodiments described herein may be executed by one or more processors, such as one or more motion processing units (MPUs), sensor processing units (SPUs), host processor(s) or core(s) thereof, digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), application specific instruction set processors (ASIPs), field programmable gate arrays (FPGAs), a programmable logic controller (PLC), a complex programmable logic device (CPLD), a discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein, or other equivalent integrated or discrete logic circuitry. The term “processor,” as used herein may refer to any of the foregoing structures or any other structure suitable for implementation of the techniques described herein. As is employed in the subject specification, the term “processor” can refer to substantially any computing processing unit or device comprising, but not limited to comprising, single-core processors; single-processors with software multithread execution capability; multi-core processors; multi-core processors with software multithread execution capability; multi-core processors with hardware multithread technology; parallel platforms; and parallel platforms with distributed shared memory. Moreover, processors can exploit nano-scale architectures such as, but not limited to, molecular and quantum-dot based transistors, switches and gates, in order to optimize space usage or enhance performance of user equipment. A processor may also be implemented as a combination of computing processing units.

In addition, in some aspects, the functionality described herein may be provided within dedicated software modules or hardware modules configured as described herein. Also, the techniques could be fully implemented in one or more circuits or logic elements. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of an SPU/MPU and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with an SPU core, MPU core, or any other such configuration.

Overview of Discussion

Discussion begins with a description of an example Piezoelectric Micromachined Ultrasonic Transducer (PMUT), in accordance with various embodiments. Example arrays including PMUT devices are then described. Example operations of the example arrays of PMUT devices are then further described. Example sensor configurations for generating a composite image having an increased image pixel density in a given density of ultrasonic transducers are then described.

A conventional piezoelectric ultrasonic transducer able to generate and detect pressure waves can include a membrane with the piezoelectric material, a supporting layer, and electrodes combined with a cavity beneath the electrodes. Miniaturized versions are referred to as PMUTs. Typical PMUTs use an edge anchored membrane or diaphragm that maximally oscillates at or near the center of the membrane at a resonant frequency (f) proportional to h/a², where h is the thickness, and a is the radius of the membrane. Higher frequency membrane oscillations can be created by increasing the membrane thickness, decreasing the membrane radius, or both. Increasing the membrane thickness has its limits, as the increased thickness limits the displacement of the membrane. Reducing the PMUT membrane radius also has limits, because a larger percentage of PMUT membrane area is used for edge anchoring.

Embodiments described herein relate to a PMUT device for ultrasonic wave generation and sensing. In accordance with various embodiments, an array of such PMUT devices is described. The PMUT includes a substrate and an edge support structure connected to the substrate. A membrane is connected to the edge support structure such that a cavity is defined between the membrane and the substrate, where the membrane is configured to allow movement at ultrasonic frequencies. The membrane includes a piezoelectric layer and first and second electrodes coupled to opposing sides of the piezoelectric layer. An interior support structure is disposed within the cavity and connected to the substrate and the membrane. In some embodiments, the interior support structure may be omitted.

The described PMUT device and array of PMUT devices can be used for generation of acoustic signals or measurement of acoustically sensed data in various applications, such as, but not limited to, medical applications, security systems, biometric systems (e.g., fingerprint sensors and/or motion/gesture recognition sensors), mobile communication systems, industrial automation systems, consumer electronic devices, robotics, etc. In one embodiment, the PMUT device can facilitate ultrasonic signal generation and sensing (transducer). Moreover, embodiments described herein provide a sensing component including a silicon wafer having a two-dimensional (or one-dimensional) array of ultrasonic transducers.

Embodiments described herein provide a PMUT that operates at a high frequency for reduced acoustic diffraction through high acoustic velocity materials (e.g., glass, metal), and for shorter pulses so that spurious secondary or undesired reflections can be time-gated out. Embodiments described herein also provide a PMUT that has a low quality factor providing a shorter ring-up and ring-down time to allow better rejection of spurious reflections by time-gating. Embodiments described herein also provide a PMUT that has a high fill-factor providing for large transmit and receive signals.

Embodiments described herein provide for generation of a composite image having an increased image pixel density in a given density of ultrasonic transducers. For instance, a first set of pixels is captured at an ultrasonic sensor using a first beamforming pattern, wherein the first beamforming pattern comprises a first pattern of ultrasonic transducers of the ultrasonic sensor. A second set of pixels is captured at the ultrasonic sensor using a second beamforming pattern, wherein the second beamforming pattern comprises a second pattern of ultrasonic transducers, wherein the second beamforming pattern is different than the first beamforming pattern, and wherein pixels of the second set of pixels correspond to positions between pixels of the first set of pixels. The first set of pixels and the second set of pixels are combined to form the composite image.

Piezoelectric Micromachined Ultrasonic Transducer (PMUT)

Systems and methods disclosed herein, in one or more aspects provide efficient structures for an acoustic transducer (e.g., a piezoelectric actuated transducer or PMUT). One or more embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. It may be evident, however, that the various embodiments can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the embodiments in additional detail.

As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. In addition, the word “coupled” is used herein to mean direct or indirect electrical or mechanical coupling. In addition, the word “example” is used herein to mean serving as an example, instance, or illustration.

FIG. 1A is a diagram illustrating a PMUT device 100 having a center pinned membrane, according to some embodiments. PMUT device 100 includes an interior pinned membrane 120 positioned over a substrate 140 to define a cavity 130. In one embodiment, membrane 120 is attached both to a surrounding edge support 102 and interior support 104. In one embodiment, edge support 102 is connected to an electric potential. Edge support 102 and interior support 104 may be made of electrically conducting materials, such as and without limitation, aluminum, molybdenum, or titanium. Edge support 102 and interior support 104 may also be made of dielectric materials, such as silicon dioxide, silicon nitride or aluminum oxide that have electrical connections on their sides or in vias through edge support 102 or interior support 104, electrically coupling lower electrode 106 to electrical wiring in substrate 140.

In one embodiment, both edge support 102 and interior support 104 are attached to a substrate 140. In various embodiments, substrate 140 may include at least one of, and without limitation, silicon or silicon nitride. It should be appreciated that substrate 140 may include electrical wirings and connection, such as aluminum or copper. In one embodiment, substrate 140 includes a CMOS logic wafer bonded to edge support 102 and interior support 104. In one embodiment, the membrane 120 comprises multiple layers. In an example embodiment, the membrane 120 includes lower electrode 106, piezoelectric layer 110, and upper electrode 108, where lower electrode 106 and upper electrode 108 are coupled to opposing sides of piezoelectric layer 110. As shown, lower electrode 106 is coupled to a lower surface of piezoelectric layer 110 and upper electrode 108 is coupled to an upper surface of piezoelectric layer 110. It should be appreciated that, in various embodiments, PMUT device 100 is a microelectromechanical (MEMS) device.

In one embodiment, membrane 120 also includes a mechanical support layer 112 (e.g., stiffening layer) to mechanically stiffen the layers. In various embodiments, mechanical support layer 140 may include at least one of, and without limitation, silicon, silicon oxide, silicon nitride, aluminum, molybdenum, titanium, etc. In one embodiment, PMUT device 100 also includes an acoustic coupling layer 114 above membrane 120 for supporting transmission of acoustic signals. It should be appreciated that acoustic coupling layer can include air, liquid, gel-like materials, or other materials for supporting transmission of acoustic signals. In one embodiment, PMUT device 100 also includes platen layer 116 above acoustic coupling layer 114 for containing acoustic coupling layer 114 and providing a contact surface for a finger or other sensed object with PMUT device 100. It should be appreciated that, in various embodiments, acoustic coupling layer 114 provides a contact surface, such that platen layer 116 is optional. Moreover, it should be appreciated that acoustic coupling layer 114 and/or platen layer 116 may be included with or used in conjunction with multiple PMUT devices. For example, an array of PMUT devices may be coupled with a single acoustic coupling layer 114 and/or platen layer 116.

FIG. 1B is identical to FIG. 1A in every way, except that the PMUT device 100′ of FIG. 1B omits the interior support 104 and thus membrane 120 is not pinned (e.g., is “unpinned”). There may be instances in which an unpinned membrane 120 is desired. However, in other instances, a pinned membrane 120 may be employed.

FIG. 2 is a diagram illustrating an example of membrane movement during activation of pinned PMUT device 100, according to some embodiments. As illustrated with respect to FIG. 2, in operation, responsive to an object proximate platen layer 116, the electrodes 106 and 108 deliver a high frequency electric charge to the piezoelectric layer 110, causing those portions of the membrane 120 not pinned to the surrounding edge support 102 or interior support 104 to be displaced upward into the acoustic coupling layer 114. This generates a pressure wave that can be used for signal probing of the object. Return echoes can be detected as pressure waves causing movement of the membrane, with compression of the piezoelectric material in the membrane causing an electrical signal proportional to amplitude of the pressure wave.

The described PMUT device 100 can be used with almost any electrical device that converts a pressure wave into mechanical vibrations and/or electrical signals. In one aspect, the PMUT device 100 can comprise an acoustic sensing element (e.g., a piezoelectric element) that generates and senses ultrasonic sound waves. An object in a path of the generated sound waves can create a disturbance (e.g., changes in frequency or phase, reflection signal, echoes, etc.) that can then be sensed. The interference can be analyzed to determine physical parameters such as (but not limited to) distance, density and/or speed of the object. As an example, the PMUT device 100 can be utilized in various applications, such as, but not limited to, fingerprint or physiologic sensors suitable for wireless devices, industrial systems, automotive systems, robotics, telecommunications, security, medical devices, etc. For example, the PMUT device 100 can be part of a sensor array comprising a plurality of ultrasonic transducers deposited on a wafer, along with various logic, control and communication electronics. A sensor array may comprise homogenous or identical PMUT devices 100, or a number of different or heterogonous device structures.

In various embodiments, the PMUT device 100 employs a piezoelectric layer 110, comprised of materials such as, but not limited to, aluminum nitride (AlN), lead zirconate titanate (PZT), quartz, polyvinylidene fluoride (PVDF), and/or zinc oxide, to facilitate both acoustic signal production and sensing. The piezoelectric layer 110 can generate electric charges under mechanical stress and conversely experience a mechanical strain in the presence of an electric field. For example, the piezoelectric layer 110 can sense mechanical vibrations caused by an ultrasonic signal and produce an electrical charge at the frequency (e.g., ultrasonic frequency) of the vibrations. Additionally, the piezoelectric layer 110 can generate an ultrasonic wave by vibrating in an oscillatory fashion that might be at the same frequency (e.g., ultrasonic frequency) as an input current generated by an alternating current (AC) voltage applied across the piezoelectric layer 110. It should be appreciated that the piezoelectric layer 110 can include almost any material (or combination of materials) that exhibits piezoelectric properties, such that the structure of the material does not have a center of symmetry and a tensile or compressive stress applied to the material alters the separation between positive and negative charge sites in a cell causing a polarization at the surface of the material. The polarization is directly proportional to the applied stress and is direction dependent so that compressive and tensile stresses results in electric fields of opposite polarizations.

Further, the PMUT device 100 comprises electrodes 106 and 108 that supply and/or collect the electrical charge to/from the piezoelectric layer 110. It should be appreciated that electrodes 106 and 108 can be continuous and/or patterned electrodes (e.g., in a continuous layer and/or a patterned layer). For example, as illustrated, electrode 106 is a patterned electrode and electrode 108 is a continuous electrode. As an example, electrodes 106 and 108 can be comprised of almost any metal layers, such as, but not limited to, aluminum (Al), titanium (Ti), molybdenum (Mo), etc., which are coupled with and on opposing sides of the piezoelectric layer 110. In one embodiment, PMUT device also includes a third electrode, as illustrated in FIG. 10 and described below.

According to an embodiment, the acoustic impedance of acoustic coupling layer 114 is selected to be similar to the acoustic impedance of the platen layer 116, such that the acoustic wave is efficiently propagated to/from the membrane 120 through acoustic coupling layer 114 and platen layer 116. As an example, the platen layer 116 can comprise various materials having an acoustic impedance in the range between 0.8 to 4 Mega Rayleigh (MRayl), such as, but not limited to, plastic, resin, rubber, Teflon, epoxy, etc. In another example, the platen layer 116 can comprise various materials having a high acoustic impedance (e.g., an acoustic impendence greater than 10 MRayl), such as, but not limited to, glass, aluminum-based alloys, sapphire, etc. Typically, the platen layer 116 can be selected based on an application of the sensor. For instance, in fingerprinting applications, platen layer 116 can have an acoustic impedance that matches (e.g., exactly or approximately) the acoustic impedance of human skin (e.g., 1.6×10⁶ Rayl). Further, in one aspect, the platen layer 116 can further include a thin layer of anti-scratch material. In various embodiments, the anti-scratch layer of the platen layer 116 is less than the wavelength of the acoustic wave that is to be generated and/or sensed to provide minimum interference during propagation of the acoustic wave. As an example, the anti-scratch layer can comprise various hard and scratch-resistant materials (e.g., having a Mohs hardness of over 7 on the Mohs scale), such as, but not limited to sapphire, glass, titanium nitride (TiN), silicon carbide (SiC), diamond, etc. As an example, PMUT device 100 can operate at 20 MHz and accordingly, the wavelength of the acoustic wave propagating through the acoustic coupling layer 114 and platen layer 116 can be 70-150 microns. In this example scenario, insertion loss can be reduced and acoustic wave propagation efficiency can be improved by utilizing an anti-scratch layer having a thickness of 1 micron and the platen layer 116 as a whole having a thickness of 1-2 millimeters. It is noted that the term “anti-scratch material” as used herein relates to a material that is resistant to scratches and/or scratch-proof and provides substantial protection against scratch marks.

In accordance with various embodiments, the PMUT device 100 can include metal layers (e.g., aluminum (Al), titanium (Ti), molybdenum (Mo), etc.) patterned to form electrode 106 in particular shapes (e.g., ring, circle, square, octagon, hexagon, etc.) that are defined in-plane with the membrane 120. Electrodes can be placed at a maximum strain area of the membrane 120 or placed at close to either or both the surrounding edge support 102 and interior support 104. Furthermore, in one example, electrode 108 can be formed as a continuous layer providing a ground plane in contact with mechanical support layer 112, which can be formed from silicon or other suitable mechanical stiffening material. In still other embodiments, the electrode 106 can be routed along the interior support 104, advantageously reducing parasitic capacitance as compared to routing along the edge support 102.

For example, when actuation voltage is applied to the electrodes, the membrane 120 will deform and move out of plane. The motion then pushes the acoustic coupling layer 114 it is in contact with and an acoustic (ultrasonic) wave is generated. Oftentimes, vacuum is present inside the cavity 130 and therefore damping contributed from the media within the cavity 130 can be ignored. However, the acoustic coupling layer 114 on the other side of the membrane 120 can substantially change the damping of the PMUT device 100. For example, a quality factor greater than 20 can be observed when the PMUT device 100 is operating in air with atmosphere pressure (e.g., acoustic coupling layer 114 is air) and can decrease lower than 2 if the PMUT device 100 is operating in water (e.g., acoustic coupling layer 114 is water).

FIG. 3 is a top view of the PMUT device 100 of FIG. 1A having a substantially square shape, which corresponds in part to a cross section along dotted line 101 in FIG. 3. Layout of surrounding edge support 102, interior support 104, and lower electrode 106 are illustrated, with other continuous layers not shown. It should be appreciated that the term “substantially” in “substantially square shape” is intended to convey that a PMUT device 100 is generally square-shaped, with allowances for variations due to manufacturing processes and tolerances, and that slight deviation from a square shape (e.g., rounded corners, slightly wavering lines, deviations from perfectly orthogonal corners or intersections, etc.) may be present in a manufactured device. While a generally square arrangement PMUT device is shown, alternative embodiments including rectangular, hexagon, octagonal, ring, circular, or elliptical are contemplated. In other embodiments, more complex electrode or PMUT device shapes can be used, including irregular and non-symmetric layouts such as chevrons or pentagons for edge support and electrodes.

FIG. 4 is a simulated topographic map 400 illustrating maximum vertical displacement of the membrane 120 of the PMUT device 100 shown in FIGS. 1A-3. As indicated, maximum displacement generally occurs along a center axis of the lower electrode, with corner regions having the greatest displacement. As with the other figures, FIG. 4 is not drawn to scale with the vertical displacement exaggerated for illustrative purposes, and the maximum vertical displacement is a fraction of the horizontal surface area comprising the PMUT device 100. In an example PMUT device 100, maximum vertical displacement may be measured in nanometers, while surface area of an individual PMUT device 100 may be measured in square microns.

FIG. 5 is a top view of another example of the PMUT device 100 of FIG. 1A having a substantially circular or ring shape, which corresponds in part to a cross section along dotted line 101 in FIG. 5. Layout of surrounding edge support 102, interior support 104, and lower electrode 106 are illustrated, with other continuous layers not shown. It should be appreciated that the term “substantially” in “substantially circular shape” is intended to convey that a PMUT device 100 is generally circle-shaped, with allowances for variations due to manufacturing processes and tolerances, and that slight deviation from a circle shape (e.g., slight deviations on radial distance from center, etc.) may be present in a manufactured device.

FIG. 6 is a top view of another example of the PMUT device 100 of FIG. 1A having a substantially hexagonal shape, which corresponds in part to a cross section along dotted line 101 in FIG. 6. Layout of surrounding edge support 102, interior support 104, and lower electrode 106 are illustrated, with other continuous layers not shown. It should be appreciated that the term “substantially” in “substantially hexagonal shape” is intended to convey that a PMUT device 100 is generally hexagon-shaped, with allowances for variations due to manufacturing processes and tolerances, and that slight deviation from a hexagon shape (e.g., rounded corners, slightly wavering lines, deviations from perfectly orthogonal corners or intersections, etc.) may be present in a manufactured device.

FIG. 7 illustrates an example two-dimensional array 700 of circular-shaped PMUT devices 701 formed from PMUT devices having a substantially circular shape similar to that discussed in conjunction with FIGS. 1A, 2 and 5. Layout of circular surrounding edge support 702, interior support 704, and annular or ring shaped lower electrode 706 surrounding the interior support 704 are illustrated, while other continuous layers are not shown for clarity. As illustrated, array 700 includes columns of circular-shaped PMUT devices 701 that are offset. However, in some embodiments, the columns of circular-shaped PMUT devices 701 are not offset. It should be appreciated that the circular-shaped PMUT devices 701 may be closer together, such that edges of the columns of circular-shaped PMUT devices 701 overlap. Moreover, it should be appreciated that circular-shaped PMUT devices 701 may contact each other. In various embodiments, adjacent circular-shaped PMUT devices 701 are electrically isolated. In other embodiments, groups of adjacent circular-shaped PMUT devices 701 are electrically connected, where the groups of adjacent circular-shaped PMUT devices 701 are electrically isolated.

FIG. 8 illustrates an example two-dimensional array 800 of square-shaped PMUT devices 801 formed from PMUT devices having a substantially square shape similar to that discussed in conjunction with FIGS. 1A, 2 and 3. Layout of square surrounding edge support 802, interior support 804, and square-shaped lower electrode 806 surrounding the interior support 804 are illustrated, while other continuous layers are not shown for clarity. As illustrated, array 800 includes columns of square-shaped PMUT devices 801 that are in rows and columns. It should be appreciated that rows or columns of the square-shaped PMUT devices 801 may be offset. Moreover, it should be appreciated that square-shaped PMUT devices 801 may contact each other or be spaced apart. In various embodiments, adjacent square-shaped PMUT devices 801 are electrically isolated. In other embodiments, groups of adjacent square-shaped PMUT devices 801 are electrically connected, where the groups of adjacent square-shaped PMUT devices 801 are electrically isolated.

FIG. 9 illustrates an example two-dimensional array 900 of hexagon-shaped PMUT devices 901 formed from PMUT devices having a substantially hexagon shape similar to that discussed in conjunction with FIGS. 1A, 2 and 6. Layout of hexagon-shaped surrounding edge support 902, interior support 904, and hexagon-shaped lower electrode 906 surrounding the interior support 904 are illustrated, while other continuous layers are not shown for clarity. It should be appreciated that rows or columns of the hexagon-shaped PMUT devices 901 may be offset. Moreover, it should be appreciated that hexagon-shaped PMUT devices 901 may contact each other or be spaced apart. In various embodiments, adjacent hexagon-shaped PMUT devices 901 are electrically isolated. In other embodiments, groups of adjacent hexagon-shaped PMUT devices 901 are electrically connected, where the groups of adjacent hexagon-shaped PMUT devices 901 are electrically isolated. While FIGS. 7, 8 and 9 illustrate example layouts of PMUT devices having different shapes, it should be appreciated that many different layouts are available. Moreover, in accordance with various embodiments, arrays of PMUT devices are included within a MEMS layer.

In operation, during transmission, selected sets of PMUT devices in the two-dimensional array can transmit an acoustic signal (e.g., a short ultrasonic pulse) and during sensing, the set of active PMUT devices in the two-dimensional array can detect an interference of the acoustic signal with an object (in the path of the acoustic wave). The received interference signal (e.g., generated based on reflections, echoes, etc. of the acoustic signal from the object) can then be analyzed. As an example, an image of the object, a distance of the object from the sensing component, a density of the object, a motion of the object, etc., can all be determined based on comparing a frequency and/or phase of the interference signal with a frequency and/or phase of the acoustic signal. Moreover, results generated can be further analyzed or presented to a user via a display device (not shown).

FIG. 10 illustrates a pair of example PMUT devices 1000 in a PMUT array, with each PMUT sharing at least one common edge support 1002. As illustrated, the PMUT devices have two sets of independent lower electrode labeled as 1006 and 1026. These differing electrode patterns enable antiphase operation of the PMUT devices 1000, and increase flexibility of device operation. In one embodiment, the pair of PMUTs may be identical, but the two electrodes could drive different parts of the same PMUT antiphase (one contracting, and one extending), such that the PMUT displacement becomes larger. While other continuous layers are not shown for clarity, each PMUT also includes an upper electrode (e.g., upper electrode 108 of FIG. 1A). Accordingly, in various embodiments, a PMUT device may include at least three electrodes.

FIGS. 11A, 11B, 11C, and 11D illustrate alternative examples of interior support structures, in accordance with various embodiments. Interior supports structures may also be referred to as “pinning structures,” as they operate to pin the membrane to the substrate. It should be appreciated that interior support structures may be positioned anywhere within a cavity of a PMUT device, and may have any type of shape (or variety of shapes), and that there may be more than one interior support structure within a PMUT device. While FIGS. 11A, 11B, 11C, and 11D illustrate alternative examples of interior support structures, it should be appreciated that these examples or for illustrative purposes, and are not intended to limit the number, position, or type of interior support structures of PMUT devices.

For example, interior supports structures do not have to be centrally located with a PMUT device area, but can be non-centrally positioned within the cavity. As illustrated in FIG. 11A, interior support 1104 a is positioned in a non-central, off-axis position with respect to edge support 1102. In other embodiments, such as seen in FIG. 11B, multiple interior supports 1104 b can be used. In this embodiment, one interior support is centrally located with respect to edge support 1102, while the multiple, differently shaped and sized interior supports surround the centrally located support. In still other embodiments, such as seen with respect to FIGS. 11C and 11D, the interior supports (respectively 1104 c and 1104 d) can contact a common edge support 1102. In the embodiment illustrated in FIG. 11D, the interior supports 1104 d can effectively divide the PMUT device into subpixels. This would allow, for example, activation of smaller areas to generate high frequency ultrasonic waves, and sensing a returning ultrasonic echo with larger areas of the PMUT device. It will be appreciated that the individual pinning structures can be combined into arrays.

FIG. 12 illustrates an embodiment of a PMUT array used in an ultrasonic fingerprint sensing system 1250. The fingerprint sensing system 1250 can include a platen 1216 onto which a human finger 1252 may make contact. Ultrasonic signals are generated and received by a PMUT device array 1200, and travel back and forth through acoustic coupling layer 1214 and platen 1216. Signal analysis is conducted using processing logic module 1240 (e.g., control logic) directly attached (via wafer bonding or other suitable techniques) to the PMUT device array 1200. It will be appreciated that the size of platen 1216 and the other elements illustrated in FIG. 12 may be much larger (e.g., the size of a handprint) or much smaller (e.g., just a fingertip) than as shown in the illustration, depending on the particular application.

In this example for fingerprinting applications, the human finger 1252 and the processing logic module 1240 can determine, based on a difference in interference of the acoustic signal with valleys and/or ridges of the skin on the finger, an image depicting epi-dermis and/or dermis layers of the finger. Further, the processing logic module 1240 can compare the image with a set of known fingerprint images to facilitate identification and/or authentication. Moreover, in one example, if a match (or substantial match) is found, the identity of user can be verified. In another example, if a match (or substantial match) is found, a command/operation can be performed based on an authorization rights assigned to the identified user. In yet another example, the identified user can be granted access to a physical location and/or network/computer resources (e.g., documents, files, applications, etc.).

In another example, for finger-based applications, the movement of the finger can be used for cursor tracking/movement applications. In such embodiments, a pointer or cursor on a display screen can be moved in response to finger movement. It is noted that processing logic module 1240 can include or be connected to one or more processors configured to confer at least in part the functionality of system 1250. To that end, the one or more processors can execute code instructions stored in memory, for example, volatile memory and/or nonvolatile memory.

FIG. 13 illustrates an integrated fingerprint sensor 1300 formed by wafer bonding a CMOS logic wafer and a MEMS wafer defining PMUT devices, according to some embodiments. FIG. 13 illustrates in partial cross section one embodiment of an integrated fingerprint sensor formed by wafer bonding a substrate 1340 CMOS logic wafer and a MEMS wafer defining PMUT devices having a common edge support 1302 and separate interior support 1304. For example, the MEMS wafer may be bonded to the CMOS logic wafer using aluminum and germanium eutectic alloys, as described in U.S. Pat. No. 7,442,570. PMUT device 1300 has an interior pinned membrane 1320 formed over a cavity 1330. The membrane 1320 is attached both to a surrounding edge support 1302 and interior support 1304. The membrane 1320 is formed from multiple layers.

Example Operation of a Two-Dimensional Array of Ultrasonic Transducers

Systems and methods disclosed herein, in one or more aspects provide for the operation of a two-dimensional array of ultrasonic transducers (e.g., an array of piezoelectric actuated transducers or PMUTs). One or more embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. It may be evident, however, that the various embodiments can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the embodiments in additional detail.

FIG. 14 illustrates an example ultrasonic transducer system 1400 with phase delayed transmission, according to some embodiments. As illustrated, FIG. 14 shows ultrasonic beam transmission and reception using a one-dimensional, five-element, ultrasonic transducer system 1400 having phase delayed inputs 1410. In various embodiments, ultrasonic transducer system 1400 is comprised of PMUT devices having a center pinned membrane (e.g., PMUT device 100 of FIG. 1A).

As illustrated, ultrasonic transducer system 1400 includes five ultrasonic transducers 1402 including a piezoelectric material and activating electrodes that are covered with a continuous stiffening layer 1404 (e.g., a mechanical support layer). Stiffening layer 1404 contacts acoustic coupling layer 1406, and in turn is covered by a platen layer 1408. In various embodiments, the stiffening layer 1404 can be silicon, and the platen layer 1408 formed from glass, sapphire, or polycarbonate or similar durable plastic. The intermediately positioned acoustic coupling layer 1406 can be formed from a plastic, epoxy, or gel such as polydimethylsiloxane (PDMS) or other material. In one embodiment, the material of acoustic coupling layer 1406 has an acoustic impedance selected to be between the acoustic impedance of layers 1404 and 1408. In one embodiment, the material of acoustic coupling layer 1406 has an acoustic impedance selected to be close the acoustic impedance of platen layer 1408, to reduce unwanted acoustic reflections and improve ultrasonic beam transmission and sensing. However, alternative material stacks to the one shown in FIG. 14 may be used and certain layers may be omitted, provided the medium through which transmission occurs passes signals in a predictable way.

In operation, and as illustrated in FIG. 14, the ultrasonic transducers 1402 labelled with an “x” are triggered to emit ultrasonic waves at an initial time. At a second time, (e.g., 1-100 nanoseconds later), the ultrasonic transducers 1402 labelled with a “y” are triggered. At a third time (e.g., 1-100 nanoseconds after the second time) the ultrasonic transducer 1402 labelled with a “z” is triggered. The ultrasonic waves transmitted at different times interfere with each other, effectively resulting in a single high intensity beam-spot 1424 that exits the platen layer 1408 at a focal point, contacts objects, such as a finger (not shown), that contact the platen layer 1408 at the beam-spot 1424, and is in part reflected back to the ultrasonic transducers. In one embodiment, the ultrasonic transducers 1402 are switched from a transmission mode to a reception mode, allowing the “z” ultrasonic transducer to detect any reflected signals 1422. In other words, the phase delay pattern of the ultrasonic transducers 1402 is symmetric about the focal point where high intensity beam 1420 exits platen layer 1408.

It should be appreciated that an ultrasonic transducer 1402 of ultrasonic transducer system 1400 may be used to transmit and/or receive an ultrasonic signal, and that the illustrated embodiment is a non-limiting example. The received signal (e.g., generated based on reflections, echoes, etc. of the acoustic signal from an object contacting or near the platen layer 1408) can then be analyzed. As an example, an image of the object, a distance of the object from the sensing component, acoustic impedance of the object, a motion of the object, etc., can all be determined based on comparing a frequency, amplitude, phase and/or arrival time of the received signal with a frequency, amplitude, phase and/or transmission time of the transmitted acoustic signal. Moreover, results generated can be further analyzed or presented to a user via a display device (not shown).

FIG. 15 illustrates another example ultrasonic transducer system 1500 with phase delayed transmission, according to some embodiments. As illustrated, FIG. 15 shows ultrasonic beam transmission and reception using a virtual block of two-dimensional, 24-element, ultrasonic transducers that form a subset of a 40-element ultrasonic transducer system 1500 having phase delayed inputs. In operation, an array position 1530 (represented by the dotted line), also referred to herein as a virtual block, includes columns 1520, 1522 and 1524 of ultrasonic transducers 1502. At an initial time, columns 1520 and 1524 of array position 1530 are triggered to emit ultrasonic waves at an initial time. At a second time (e.g., several nanoseconds later), column 1522 of array position 1530 is triggered. The ultrasonic waves interfere with each other, substantially resulting in emission of a high intensity ultrasonic wave centered on column 1522. In one embodiment, the ultrasonic transducers 1502 in columns 1520 and 1524 are switched off, while column 1522 is switched from a transmission mode to a reception mode, allowing detection of any reflected signals.

In one embodiment, after the activation of ultrasonic transducers 1502 of array position 1530, ultrasonic transducers 1502 of another array position 1532, comprised of columns 1524, 1526, and 1528 of ultrasonic transducers 1502 are triggered in a manner similar to that described in the foregoing description of array position 1530. In one embodiment, ultrasonic transducers 1502 of another array position 1532 are activated after a detection of a reflected ultrasonic signal at column 1522 of array position 1530. It should be appreciated that while movement of the array position by two columns of ultrasonic transducers is illustrated, movement by one, three, or more columns rightward or leftward is contemplated, as is movement by one or more rows, or by movement by both some determined number of rows and columns. In various embodiments, successive array positions can be either overlapping in part, or can be distinct. In some embodiments, the size of array positions can be varied. In various embodiments, the number of ultrasonic transducers 1502 of an array position for emitting ultrasonic waves can be larger than the number of ultrasonic transducers 1502 of an array position for ultrasonic reception. In still other embodiments, array positions can be square, rectangular, ellipsoidal, circular, or more complex shapes such as crosses.

Example ultrasonic transducer system 1500 is operable to beamform a line of a high intensity ultrasonic waves over column 1522. It should be appreciated that the principles illustrated in FIG. 15 for beamforming a line using columns of ultrasonic transducers is applicable to embodiments for beamforming a point using ultrasonic transducers driven by two-dimensional phase-delayed transmit signals, as will be explained below. For instance, example ultrasonic transducer system 1500 includes columns of ultrasonic transducers in which the ultrasonic transducers of each column are jointly operated to activate at the same time, operating to beamform along a line. It should be appreciated that the ultrasonic transducers of a two-dimensional array may be independently operable, and used for beamform points as well, as will be described below.

FIG. 16 illustrates an example phase delay pattern for ultrasonic signal transmission of a 9×9 ultrasonic transducer block 1600 of a two-dimensional array of ultrasonic transducers, according to some embodiments. As illustrated in FIG. 16, each number in the ultrasonic transducer array is equivalent to the nanosecond delay used during operation, and an empty element (e.g., no number) in the ultrasonic transducer block 1600 means that an ultrasonic transducer is not activated for signal transmission during operation. In various embodiments, ultrasonic wave amplitude can be the same or similar for each activated ultrasonic transducer, or can be selectively increased or decreased relative to other ultrasonic transducers. In the illustrated pattern, initial ultrasonic transducer activation is limited to corners of ultrasonic transducer block 1600, followed 10 nanoseconds later by a rough ring around the edges of ultrasonic transducer block 1600. After 23 nanoseconds, an interior ring of ultrasonic transducers is activated. Together, the twenty-four activated ultrasonic transducers generate an ultrasonic beam centered on the ultrasonic transducer block 1600. In other words, the phase delay pattern of ultrasonic transducer block 1600 is symmetric about the focal point above the center of the 9×9 transducer block where a high intensity beam-spot contacts an object.

It should be appreciated that different ultrasonic transducers of ultrasonic transducer block 1600 may be activated for receipt of reflected ultrasonic signals. For example, the center 3×3 ultrasonic transducers of ultrasonic transducer block 1600 may be activated to receive the reflected ultrasonic signals. In another example, the ultrasonic transducers used to transmit the ultrasonic signal are also used to receive the reflected ultrasonic signal. In another example, the ultrasonic transducers used to receive the reflected ultrasonic signals include at least one of the ultrasonic transducers also used to transmit the ultrasonic signals.

FIG. 17 illustrates another example phase delay pattern for a 9×9 ultrasonic transducer block 1700, according to some embodiments. As illustrated in FIG. 17, the example phase delay pattern utilizes equidistant spacing of transmitting ultrasonic transducers. As illustrated in FIG. 16, each number in the ultrasonic transducer array is equivalent to the nanosecond delay used during operation, and an empty element (e.g., no number) in the ultrasonic transducer block 1700 means that an ultrasonic transducer is not activated for signal transmission during operation. In the illustrated embodiment, the initial ultrasonic transducer activation is limited to corners of ultrasonic transducer block 1700, followed 11 nanoseconds later by a rough ring around the edges of ultrasonic transducer block 1700. After 22 nanoseconds, an interior ring of ultrasonic transducers is activated. The illustrated embodiment utilizes equidistant spacing of the transmitting ultrasonic transducers to reduce issues with crosstalk and heating, wherein each activated ultrasonic transducers is surrounded by un-activated ultrasonic transducers. Together, the twenty-four activated ultrasonic transducers generate an ultrasonic beam centered over the ultrasonic transducer block 1700.

FIG. 18 illustrates a plan view 1800 of simulated ultrasonic pressure on the focal plane for an example ultrasonic transducer system using three timing phases, according to an embodiment. FIG. 18 is a graphical illustration of simulated ultrasonic intensity for a three-phase system such as discussed with respect to FIG. 17. In this embodiment, the contour lines illustrate creation of a high intensity centrally located beam capable of directing an approximately ˜50 to 100 um spot at a platen layer. The illustrated beam linearly adds the energy from all 24 actuated ultrasonic transducers and has a 3 dB beam width of 73 um.

FIG. 19 illustrates a cross section 1900 of simulated ultrasonic pressure on the focal plane for an example ultrasonic transducer system using either three or five timing phases, according to an embodiment. FIG. 19 is a graphical illustration of a cross section 1900 at line 1810 of FIG. 18 of the simulated ultrasonic intensity for a three-phase system such as discussed with respect to FIG. 17. Also shown in FIG. 19 is an example of the concentrated beam formed using five timing phases and twenty-five actuated ultrasonic transducers, which illustrates nominally better performance but at increased complexity.

FIGS. 20A-C illustrate example transmitter blocks and receiver blocks for an array position in a two-dimensional array 2000 of ultrasonic transducers, according to some embodiments. In FIG. 20A, a four phase (indicated using different hatch patterns) activated phase delay pattern of ultrasonic transducers in a 9×9 array position 2010 is used to generate an ultrasonic beam. Example receiver patterns are also illustrated, with receive pattern 2020 being ultrasonic transducers in a 5×5 square and receive pattern 2022 being a more complex cross shaped block.

In FIG. 20B, the 9×9 array position 2012 is moved rightward by a single column 2032 relative to array position 2010 of FIG. 20A, as indicated by the arrow. In other words, after activation at array position 2010 of two-dimensional array 2000, array position 2012 of two-dimensional array 2000 is activated, effectively sensing a pixel to the right of two-dimensional array 2000. In such a manner, multiple pixels associated with multiple array positions of the two-dimensional array 2000 can be sensed. Similarly, in FIG. 20C the 9×9 array position 2014 is moved downward by a single row 2034 relative to array position 2010 of FIG. 20A after activation of array position 2010 of two-dimensional array 2000, as indicated by the arrow. It should be appreciated that the 9×9 array position can move to different positions of two-dimensional array 2000 in any sequence. For example, an activation sequence may be defined as left to right for a row of ultrasonic transducers, then moving down one row when the end of a row is reached, and continuing to proceed in this manner until a desired number of pixels are sensed. In another example, the activation sequence may be defined as top to bottom for a column, and moving to another column once enough pixels have been sensed for a column. It should be appreciated that any activation sequence may be defined without limitation, including a random activation sequence. Moreover, it should be appreciated that any number of columns and/or rows can be skipped depending on a desired resolution.

In various embodiments, as an array position approaches an edge of two-dimensional array 2000, only those ultrasonic transducers that are available in two-dimensional array 2000 are activated. In other words, where a beam is being formed at a center of an array position, but the center is near or adjacent an edge of two-dimensional array 2000 such that at least one ultrasonic transducer of a phase delay pattern is not available (as the array position extends over an edge), then only those ultrasonic transducers that are available in two-dimensional array 2000 are activated. In various embodiments, the ultrasonic transducers that are not available (e.g., outside the edge of two-dimensional array 2000) are truncated from the activation pattern. For example, for a 9×9 ultrasonic transducer block, as the center ultrasonic transducer moves towards the edge such that the 9×9 ultrasonic transducer block extends over the edge of the two-dimensional array, rows, columns, or rows and columns (in the instance of corners) of ultrasonic transducers are truncated from the 9×9 ultrasonic transducer block. For instance, a 9×9 ultrasonic transducer block effectively becomes a 5×9 ultrasonic transducer block when the center ultrasonic transducer is along an edge of the two-dimensional array. Similarly, a 9×9 ultrasonic transducer block effectively becomes a 6×9 ultrasonic transducer block when the center ultrasonic transducer is one row or column from an edge of the two-dimensional array. In other embodiments, as an array position approaches an edge of two-dimensional array 2000, the beam is steered by using phase delay patterns that are asymmetric about the focal point, as described below in accordance with FIGS. 21 through 25B.

FIG. 21 illustrates an example ultrasonic transducer system 2100 with phase delayed transmission, according to some embodiments. FIG. 21 shows five different modes of ultrasonic beam transmission using an example one-dimensional, fifteen-element, ultrasonic transducer system 2100 having phase delayed inputs. As illustrated, ultrasonic transducers 2102 can be operated in various modes to provide ultrasonic beam spots focused along line 2150 (e.g., a top of a platen layer). In a first mode, a single ultrasonic transducer 2152 is operated to provide a single broad ultrasonic beam having a peak amplitude centered on arrow 2153. In a second mode, multiple ultrasonic transducers in a symmetrical pattern 2154 about the center ultrasonic transducer are sequentially triggered to emit ultrasonic waves at differing initial times. As illustrated, a center located transducer is triggered at a delayed time with respect to surrounding transducers (which are triggered simultaneously). The ultrasonic waves interfere with each other, resulting in a single high intensity beam 2155. In a third mode, for ultrasonic transducers 2156 located adjacent to or near an edge of the ultrasonic transducer system 2100, an asymmetrical triggering pattern can be used to produce beam 2157. In a fourth mode, asymmetrical triggering patterns for transducers 2158 can be used to steer an ultrasound beam to an off-center location 2159. A shown, the focused beam 2159 can be directed to a point above and outside boundaries of the ultrasonic transducer system 2100. In a fifth mode, the beam can be steered to focus at a series of discrete positions, with the beam spacing having a pitch less than, equal to, or greater than a pitch of the ultrasonic transducers. In FIG. 21, transducers 2160 are triggered at separate times to produce beam spots separated by a pitch less than that of the ultrasonic transducers (indicated respectively by solid lines directed to form beam spot 2161 and dotted lines to form beam spot 2163).

FIG. 22 illustrates an example ultrasonic transducer system 2200 with phase delayed transmission, according to some embodiments. As illustrated, FIG. 22 shows ultrasonic beam transmission and reception using a one-dimensional, three-element, ultrasonic transducer system 2200 having phase delayed inputs 2210. In various embodiments, ultrasonic transducer system 2200 is comprised of PMUT devices having a center pinned membrane (e.g., PMUT device 100 of FIG. 1A).

As illustrated, ultrasonic transducer system 2200 includes three ultrasonic transducers 2202 including a piezoelectric material and activating electrodes that are covered with a continuous stiffening layer 2204 (e.g., a mechanical support layer). Stiffening layer 2204 contacts acoustic coupling layer 2206, and in turn is covered by a platen layer 2208. In various embodiments, the stiffening layer 2204 can be silicon, and the platen layer 2208 formed from glass, sapphire, or polycarbonate or similar durable plastic. The intermediately positioned acoustic coupling layer 2206 can be formed from a plastic or gel such as PDMS or other material. In one embodiment, the material of acoustic coupling layer 2206 has an acoustic impedance selected to be between the acoustic impedance of layers 2204 and 2208. In one embodiment, the material of acoustic coupling layer 2206 has an acoustic impedance selected to be close the acoustic impedance of platen layer 2208, to reduce unwanted acoustic reflections and improve ultrasonic beam transmission and sensing. However, alternative material stacks to the one shown in FIG. 22 may be used and certain layers may be omitted, provided the medium through which transmission occurs passes signals in a predictable way.

In operation, and as illustrated in FIG. 22, the ultrasonic transducer 2202 labelled with an “x” is triggered to emit ultrasonic waves at an initial time. At a second time, (e.g., 1-100 nanoseconds later), the ultrasonic transducer 2202 labelled with a “y” is triggered. At a third time (e.g., 1-100 nanoseconds after the second time) the ultrasonic transducer 2202 labelled with a “z” is triggered. The ultrasonic waves transmitted at different times cause interference with each other, effectively resulting in a single high intensity beam-spot 2224 that exits the platen layer 2208, contacts objects, such as a finger (not shown), that contact the platen layer 2208, and is in part reflected back to the ultrasonic transducers 2202. In one embodiment, the ultrasonic transducers 2202 are switched from a transmission mode to a reception mode, allowing the “z” ultrasonic transducer to detect any reflected signals. In other words, the phase delay pattern of the ultrasonic transducers 2202 is asymmetric about the focal point where high intensity beam 2220 exits platen layer 2208.

It should be appreciated that an ultrasonic transducer 2202 of ultrasonic transducer system 2200 may be used to transmit and/or receive an ultrasonic signal, and that the illustrated embodiment is a non-limiting example. The received signal (e.g., generated based on reflections, echoes, etc. of the acoustic signal from an object contacting or near the platen layer 2208) can then be analyzed. As an example, an image of the object, a distance of the object from the sensing component, an acoustic impedance of the object, a motion of the object, etc., can all be determined based on comparing a frequency, amplitude and/or phase of the received interference signal with a frequency, amplitude and/or phase of the transmitted acoustic signal. Moreover, results generated can be further analyzed or presented to a user via a display device (not shown).

FIG. 23 illustrates another example ultrasonic transducer system 2300 with phase delayed transmission, according to some embodiments. As illustrated, FIG. 23 shows ultrasonic beam transmission and reception using a virtual block of two-dimensional, 16-element, ultrasonic transducers that form a subset of a 32-element ultrasonic transducer system 2300 having phase delayed inputs. In operation, an array position 2330 (represented by the dotted line), also referred to herein as a virtual block, includes columns 2322 and 2324 of ultrasonic transducers 2302. At an initial time, column 2324 of array position 2330 is triggered to emit ultrasonic waves at an initial time. At a second time (e.g., several nanoseconds later), column 2322 of array position 2330 is triggered. The ultrasonic waves interfere with each other, substantially resulting in emission of a high intensity ultrasonic plane wave centered on column 2322. In one embodiment, the ultrasonic transducers 2302 in column 2324 is switched off, while column 2322 is switched from a transmission mode to a reception mode, allowing detection of any reflected signals.

In one embodiment, after the activation of ultrasonic transducers 2302 of array position 2330, ultrasonic transducers 2302 of another array position 2332, comprised of columns 2324, 2326, and 2328 of ultrasonic transducers 2302 are activated. In operation, at an initial time, columns 2324 and 2328 of array position 2332 are triggered to emit ultrasonic waves at an initial time. At a second time (e.g., several nanoseconds later), column 2326 of array position 2332 is triggered. The ultrasonic waves interfere with each other, substantially resulting in emission of a high intensity ultrasonic plane wave centered on column 2326. In one embodiment, the ultrasonic transducers 2302 in columns 2324 and 2328 are switched off, while column 2326 is switched from a transmission mode to a reception mode, allowing detection of any reflected signals. In one embodiment, ultrasonic transducers 2302 of another array position 2332 are activated after a detection of a reflected ultrasonic signal at column 2322 of array position 2330. It should be appreciated that while movement of the array position by two columns of ultrasonic transducers is illustrated, movement by one, three, or more columns rightward or leftward is contemplated, as is movement by one or more rows, or by movement by both some determined number of rows and columns. In various embodiments, successive array positions can be either overlapping in part, or can be distinct. In some embodiments, the size of array positions can be varied. In various embodiments, the number of ultrasonic transducers 2302 of an array position for emitting ultrasonic waves can be larger than the number of ultrasonic transducers 2302 of an array position for ultrasonic reception. In still other embodiments, array positions can be square, rectangular, ellipsoidal, circular, or more complex shapes such as crosses.

Example ultrasonic transducer system 2300 is operable to beamform a line of a high intensity ultrasonic wave centered over a column of ultrasonic transducers. It should be appreciated that the principles illustrated in FIG. 23 for beamforming a line using columns of ultrasonic transducers is applicable to embodiments for beamforming a point using ultrasonic transducers, as will be explained below. For instance, example ultrasonic transducer system 2300 includes columns of ultrasonic transducers in which the ultrasonic transducers of each column are jointly operated to activate at the same time, operating to beamform along a line. It should be appreciated that the ultrasonic transducers of a two-dimensional array may be independently operable, and used for beamform points as well, as will be described below.

FIGS. 24A, 24B, 25A and 25B illustrate example phase delay patterns for a 5×5 ultrasonic transducer blocks, according to some embodiments. As illustrated in 24A, 24B, 25A and 25B, each number in the ultrasonic transducer array is equivalent to the nanosecond delay used during operation, and an empty element (e.g., no number) in the ultrasonic transducer blocks 2400, 2410, 2500 and 2510 means that an ultrasonic transducer is not activated for signal transmission during operation. In various embodiments, ultrasonic wave amplitude can be the same or similar for each activated ultrasonic transducer, or can be selectively increased or decreased relative to other ultrasonic transducers. It should be appreciated that the phase delay patterns described in accordance with FIGS. 24A, 24B, 25A and 25B are asymmetric about the focal point where the resulting Tx beam-spot contacts an object.

FIG. 24A illustrates an example phase delay pattern for an array position of ultrasonic transducers at an edge of a two-dimensional array of ultrasonic transducers. Because ultrasonic transducer block 2400 is located at an edge, a symmetrical phase delay pattern about a center of ultrasonic transducer block 2400 is not available. In the illustrated pattern, initial ultrasonic transducer activation is limited to rightmost corners of the array, followed by selected action of ultrasonic transducers at 1, 4, 5, 6, and 8 nanosecond intervals. Together, the activated ultrasonic transducers generate an ultrasonic beam centered on the 8 nanosecond delayed ultrasonic transducer indicated in gray. In one embodiment, so as to reduce issues with crosstalk and heating, each activated ultrasonic transducer is equidistant from each other, being surrounded by un-activated ultrasonic transducer.

FIG. 24B illustrates an example phase delay pattern for a 5×5 ultrasonic transducer block 2410 in a corner of a two-dimensional array of ultrasonic transducers, with equidistant spacing of transmitting ultrasonic transducers. Like the phase delay timing pattern of FIG. 24A, the initial ultrasonic transducer activation is asymmetrical. Together, the activated ultrasonic transducers generate an ultrasonic beam centered on the 8 nanosecond delayed ultrasonic transducer indicated in gray. Adjacent ultrasonic transducers are activated in this embodiment to increase beam intensity.

FIG. 25A illustrates an example phase delay pattern for an array position of ultrasonic transducers at an edge of a two-dimensional array of ultrasonic transducers. Because ultrasonic transducer block 2500 is located at an edge, a symmetrical phase delay pattern about a center of ultrasonic transducer block 2500 is not available. In the illustrated pattern, initial ultrasonic transducer activation is limited to rightmost corners of the array, followed by selected action of ultrasonic transducers at 1, 4, 5, 6, and 8 nanosecond intervals. Together, the activated ultrasonic transducers generate an ultrasonic beam centered on the 8 nanosecond delayed ultrasonic transducer indicated in gray. After beam transmit concludes, the gray (8 nanosecond) ultrasonic transducer is switched into a receive mode, along with those surrounding ultrasonic transducers indicated by spotted gray.

FIG. 25B illustrates ultrasonic transducer block 2510 is located at an edge of a two-dimensional array of ultrasonic transducers. This pattern is formed as ultrasonic transducer block 2500 is moved up a single row of ultrasonic transducers (indicated by arrow 2502) with respect to the phase delay pattern illustrated in FIG. 25A. As in FIG. 25A, the activated ultrasonic transducers together generate an ultrasonic beam centered on the 8 nanosecond delayed ultrasonic transducer indicated in gray. After beam transmit concludes, the gray (8 nanosecond) ultrasonic transducer is switched into a receive mode, along with those surrounding ultrasonic transducers indicated by spotted gray.

FIG. 26 illustrates example simultaneous operation of transmitter blocks for a multiple array positions in a two-dimensional array 2600 of ultrasonic transducers, according to some embodiments. As described above, a 9×9 array position can be used as a beamforming array for an ultrasound transducer. In the illustrated example, two-dimensional array 2600 is 48×144 ultrasonic transducers, separated into twelve identical 24×24 blocks. In one embodiment, a mux-based transmission/receive (Tx/Rx) timing control method can be used to activate the appropriate ultrasonic transducers in each block. When a sequence of activation to generate an ultrasound beam and sensing reflected echoes is completed, the 9×9 array position is moved rightward or leftward, or upward and downward, with respect to the drawing, and the sequence is repeated until substantially all ultrasonic transducers have emitted an ultrasonic beam.

The PMUT sensor array can be comprised of 144×48 PMUT transducers arranged into a rectangular grid 2600 as shown in FIG. 26. However, this is but one example of how the PMUT transducers may be arranged. Because the PMUT dimensions in this example are set at 70 μm×70 μm, the resulting sensor array area is 10.80 mm×3.36 mm. To allow for consistent referencing of locations within the array, the long dimension is defined herein as the X-axis, the short dimension as the Y-axis, and bottom left corner as the origin. As such (using units of PMUTs as the coordinate system), the PMUT at the bottom left corner is at position (0, 0) whereas the one at the top right corner is at position (143, 47).

The two-dimensional array depicted in FIG. 26 comprises a 6×2 array of sub-blocks 2602, each block comprising an array of 24×24 ultrasonic transducers, thereby providing a total of 144×48 ultrasonic transducers in the rectangular grid 2600. In another example, a 5×2 array of sub-blocks can be used, each block comprising an array of 27×23 ultrasonic transducers, thereby providing a total of 135×46 ultrasonic transducers in the rectangular grid. The resulting sensor array area would be 9.45 mm×3.22 mm.

In order to capture fingerprint images as quickly as possible, it is desired to simultaneously image as many pixels as possible. This is limited in practice by power consumption, number of independent receiver (Rx) channels (slices) and analog-to-digital converters (ADCs), and spacing requirements between active PMUTs required to avoid interference. Accordingly, the capability to simultaneously capture several image pixels, e.g., 12 image pixels, may be implemented. It will be appreciated that fewer than 12 or more than 12 image pixels may be captured simultaneously. In an embodiment, this involves 12 independent, parallel receiver channels and ADCs. Each of these receiver channels and ADCs is associated with a subset of the overall sensor array as shown in FIG. 26. In this example, the 12 “PMUT Blocks” 2602 (also referred to as “ADC areas” or “array sub-blocks”) are 24×24 PMUTs in size. Thus, the ultrasonic sensor may comprise a number, here, 12, of blocks of ultrasonic transducers.

The 12 Rx channels and ADCs are placed directly above or below each associated array sub-block. During a typical imaging operation, each array sub-block 2602 is configured and operated identically such that 12 image pixels are captured simultaneously, one each from identical locations within each array sub-block. A pattern of transmit (Tx) phases is applied to selected PMUTs within each of the array sub-blocks 2602. The Tx phases are arranged to focus ultrasonic energy onto the area just above the center of each of the patterns—a process called transmit beamforming. The ultrasonic signal that is reflected back to the PMUTs at the center of each pattern is converted to an electrical signal and routed to the associated Rx channel and ADC for sensing and storage. The overall process of transmitting an ultrasonic signal, waiting for it to propagate to the target and back, and capturing the reflected ultrasonic signal is referred to herein as a “TxRx Period”.

Imaging over the entire sensor area is accomplished by stepping the Tx beamforming patterns over the entire PMUT array, transmitting and receiving at each location corresponding to an image pixel. Because 12 image pixels are captured simultaneously during each TxRx Period (one image pixel from identical locations within each array sub-block 2602), it takes just as much time to capture the image pixels for the entire array as it would to capture the image pixels for only a single array sub-block.

There may be times when scanning is required over only a sub-set of the array sub-blocks. In such cases, it is possible to disable transmitting or receiving signals within designated array sub-blocks to save the power that would otherwise be used in transmitting or receiving within those sub-blocks. In one embodiment, the array is configured (e.g., via a register) to enable transmitting in all 12 array sub-blocks. In other embodiments, the array is configured to disable transmit within selected vertical pairs of array sub-blocks. For example, setting bits of a transmit register to 1_0111 keeps array sub-blocks 0-5, 8, and 9 active for transmit but shuts off transmit in array sub-blocks 6 and 7. Similarly, the array is configured (e.g., via a register) to enable receiving in all 12 array sub-blocks. However, selected bits of this register can be set to “0” to disable receive within selected array sub-blocks. For example, setting bits of a receive register to 1101_1011_1111 enables all the array sub-blocks to receive normally except for array sub-blocks 6 and 9 (all receiver and ADC circuitry associated with array blocks 6 and 9 are powered down).

As previously described, it should be appreciated that any type of activation sequence may be used (e.g., side-to-side, top-to-bottom, random, another predetermined order, row and/or column skipping, etc.) Moreover, it should be appreciated that FIG. 26 illustrates a phase delay pattern that is symmetric about a focal point of the transmitting pixels. As previously described, it is understood that different phase delay patterns may be used as a focal point approaches or is adjacent to an edge and/or corner of the two-dimensional array. For example, a phase delay pattern similar to that illustrated in FIG. 24A may be used as a focal point approaches or is adjacent to an edge of the two-dimensional array and a phase delay pattern similar to that illustrated in FIG. 24B may be used as a focal point approaches or is adjacent to corner of the two-dimensional array. In various embodiments, the ultrasonic transducers that are not available (e.g., outside the edge of a two-dimensional array 2600) are truncated from the activation pattern. For example, for a 9×9 array position, as the center ultrasonic transducer moves towards an edge such that the 9×9 array position extends over the edge of the two-dimensional array, rows, columns, or rows and columns (in the instance of corners) of ultrasonic transducers are truncated from the 9×9 array position. For instance, a 9×9 array position effectively becomes a 5×9 array position when the center ultrasonic transducer is along an edge of the two-dimensional array. Similarly, a 9×9 ultrasonic transducer block effectively becomes a 6×9 array position when the center ultrasonic transducer is one row or column from an edge of the two-dimensional array.

FIG. 27 illustrates an example operational model 2700 of a transmit signal to a receive signal of a two-dimensional array of ultrasonic transducers, according to some embodiments. FIG. 27 shows an operational model 2700 from voltage transmit signal into a PMUT array 2710 and ending with voltage receive signal from the PMUT array 2760. Three cycles of the voltage waveform are effectively bandpass filtered by the PMUT 2720, sent out as an ultrasonic pressure signal 2730 that is attenuated and delayed by interaction with an object 2740, and then bandpass filtered by the PMUT array 2750 to create the final receive signal 2760. In the illustrated example, the PMUT bandpass filter response 2720 and 2750 is assumed to be centered at 50 MHz with Q of approximately 3, although other values may be used.

FIG. 28 illustrates an example transmit path architecture 2800 of a two-dimensional array of ultrasonic transducers, according to some embodiments. Achieving two-dimensional beamforming with high image resolution under glass uses relatively high ultrasonic frequencies and precise timing. Electronics to support a PMUT array with a center frequency of 50 MHz and a beamforming timing resolution of 1 nanosecond can be used. The 50 MHz frequency can be generated by an on-chip RC oscillator and PLL that can be trimmed for sufficient accuracy by an off-chip clock source. The beamforming resolution can be set by an on-chip PLL that outputs several timing phases that correspond to ˜3 cycles of 50 MHz frequency and are appropriately delayed with respect to each other. These phases can be routed to each PMUT according to the sel_(ph_map) signals shown in the FIG. 28.

FIG. 29 illustrates an example receive path architecture of a two-dimensional array of ultrasonic transducers, according to some embodiments. The select lines 2910 correspond to rxColsel[k] for receive, and the select lines 2920 correspond to rxRowsel[k] for receive. Multiple PMUTs can be selected together for receiving the signal. The signal from the PMUTs is fed into a front end receiver. The signal is then filtered to reduce noise outside of the signal bandwidth. The filtered signal is then integrated and digitized with an ADC. In some embodiments, the PMUT and receiver layout allow straightforward extension of the PMUT array size, since different applications can require different sensor array areas. The number of receiver slices will be determined by the desired PMUT array size and minimum ultrasonic transducer separation between transmit beams. For example, in one embodiment, a 20 ultrasonic transducer minimum separation between adjacent sets of active ultrasonic transducers reduces crosstalk.

Image Resolution

In some embodiments, a two-dimensional array of individual PMUT devices (e.g., PMUT device 100 of FIG. 1A or 100′ of FIG. 1B) corresponds with a two-dimensional array of control electronics. This embodiment also applies to other types of MEMS arrays with integrated control electronics. This includes, but is not limited to, applications for inertial sensors, optical devices, display devices, pressure sensors, microphones, inkjet printers, and other applications of MEMS technology with integrated mixed-signal electronics for control. It should be appreciated that while the described embodiments may refer CMOS control elements for controlling MEMS devices and/or PMUT devices, that the described embodiments are not intended to be limited to such implementations.

The placement of the PMUT sensors into an array with a pitch of 70 μm naturally leads to an image pixel density of 1/70 μm=363 dpi, where one image pixel is captured at each PMUT location. This image pixel density may be sufficient for many applications, especially since image pixel density is only one of several factors affecting image resolution (other factors include ultrasonic characteristics of the materials between the PMUTs and the finger, ultrasonic frequency, Tx beamforming pattern, etc.). As such, the actual image resolution may be less than the image pixel density.

On the other hand, some applications may require higher image pixel density than that naturally provided by the PMUT density. To address such applications, the teachings herein enable the capture of higher pixel densities by using Tx beamforming to focus the ultrasonic energy at locations other than directly above the center of a PMUT. This is illustrated in FIGS. 30A-30C. In an embodiment, in FIGS. 30A-30B, X=Y=70 μm. FIG. 30A shows the pixel image density ( 1/70 μm=363 dpi) 3000 that results when the Tx beamforming is arranged such that the ultrasonic energy is focused directly above the center 3002 of a PMUT. The image pixels in a 3.50 mm×9.45 mm area=(50×135)=6750. In FIGS. 30A-30C, the centers of the PMUTs are indicated by open circles.

FIG. 30B shows the pixel image density (1/49.5 μm=513 dpi) 3020 that results when Tx beamforming is arranged such that the ultrasonic energy is focused both directly above the center 3002 of a PMUT and at the corner 3004 between four adjacent PMUTs. The distance “a” between nearest pixels 3002 a, 3004 a is 49.5 μm for 70 μm spacing. Capturing this higher image pixel density is possible by operating the sensor to capture two scans per image. The first scan uses a Tx beamforming pattern that is X-Y symmetrical around a target PMUT center 3002 to capture image pixels directly above the PMUT centers. The second scan uses a different Tx beamforming pattern that is X-Y symmetrical around a target PMUT corner 3004 to capture image pixels directly above the PMUT corners. The image data from the two scans are then combined to form a composite image with an image pixel density that is twice as high as that of each individual scan. It is noted that the dpi is only √2 times higher than each of the two individual scans because this is a linear metric rather than an area metric. The image pixels in a 3.50 mm×9.45 mm area=(50×135)+(49×134)=13,316.

While an example spacing between pixels is given above as 70 μm, it is to be understood that the principles disclosed herein apply to other pixel spacings, including, but not limited to, 100 μm and 50 μm. This is also true of pixel image density, which is the inverse of pitch.

FIG. 30C shows the pixel image density ( 1/50 μm=508 dpi) 3040 generated from an array of PMUTs having a spacing of X′=Y′=100 μm. In this example, four scans per image are used. Here, the Tx beamforming is arranged such that the ultrasonic energy is focused (1) above the center 3002 of a PMUT, (2) at the corner 3004 between four adjacent PMUTs, (3) at a midpoint of a first edge 3006 x along an X axis between two adjacent ultrasonic transducers and (4) at a midpoint of a second edge 3006 y along a Y axis between two other adjacent ultrasonic transducers, where the second axis is orthogonal to the first axis. The distance “a” between nearest pixels 3002 a, 3006 x or 3001 a, 3006 y is 50 μm for 100 μm spacing. Capturing this higher image pixel density is possible by operating the sensor to capture four scans per image. The first scan uses a Tx beamforming pattern that is X-Y symmetrical around a target PMUT center 3002 to capture image pixels directly above the PMUT centers. The second scan uses a different Tx beamforming pattern that is X-Y symmetrical around a target PMUT corner 3004 to capture image pixels directly above the PMUT corners. The third scan uses yet a different Tx beamforming pattern that is X-Y symmetrical around a target PMUT edge midpoint 3006 x. The fourth scan uses a still different Tx beamforming pattern that is X-Y symmetrical around a target PMUT edge midpoint 3006 y, where the edge midpoint 3006 x is orthogonal to, or different than, the edge midpoint 3006 y. The image data from the four scans are then combined to provide a composite image with an image pixel density that is four times as high as that of each individual scan. Here, the PMUTs have a relaxed spacing (100 μm) as compared with the spacing (70 μm) in FIG. 30A. Yet, the image pixel density is twice that of the array 3000 shown in FIG. 30A: the image pixels in a 3.50 mm×9.45 mm area=(69×189)=13,041.

FIGS. 30A-30C are based on a two-dimensional array 800 of square-shaped PMUT devices 801 formed from PMUT devices having a substantially square shape, such as shown in FIG. 8. A similar approach to increase the image pixel density can be performed for a two-dimensional array 900 of hexagon-shaped PMUT devices 901 formed from PMUT devices having a substantially hexagon shape, such as depicted in FIG. 9. FIGS. 31A-31B depict a method for capturing higher pixel densities by using Tx beamforming to focus the ultrasonic energy at locations other than directly above the center of a PMUT. FIG. 31A shows the pixel image density 3100 that results when the Tx beamforming is arranged such that the ultrasonic energy is focused directly above the center 3202 of a PMUT. In FIGS. 31A-31B, the centers of the PMUTs are indicated by open circles.

FIG. 31B shows the pixel image density 3120 that results when Tx beamforming is arranged such that the ultrasonic energy is focused both directly above the center 3102 of a PMUT and at the corners 3104 between three adjacent PMUTs. Capturing a higher image pixel density is possible by operating the sensor to capture two scans per image. The first scan uses a Tx beamforming pattern that is X-Y symmetrical around a target PMUT center 3102 to capture image pixels directly above the PMUT centers. The second scan uses a different Tx beamforming pattern that is X-Y symmetrical around a target PMUT corner 3104 to capture image pixels directly above the PMUT corners. The image data from the two scans are then combined to form a composite image with an image pixel density that is three times as high as that of each individual scan. It will be appreciated that the PMUTs themselves do not need to be hexagonal but simply need to be arranged as shown in either FIG. 7 or 9.

FIG. 32 illustrates a flow diagram 3200 of an example method for generating a composite image having an increased image pixel density in a given density of ultrasonic transducers, according to various embodiments. Procedures of this method will be described with reference to elements and/or components of various figures described herein. It is appreciated that in some embodiments, the procedures may be performed in a different order than described, that some of the described procedures may not be performed, and/or that one or more additional procedures to those described may be performed. Flow diagram 3200 includes some procedures that, in various embodiments, are carried out by one or more processors under the control of computer-readable and computer-executable instructions that are stored on non-transitory computer-readable storage media. It is further appreciated that one or more procedures described in flow diagram 3200 may be implemented in hardware, or a combination of hardware with firmware and/or software.

The image pixel density may be increased by the following method 3200 depicted in FIG. 32: first, capture 3205 a first set of pixels at an ultrasonic sensor using a first beamforming pattern, wherein the first beamforming pattern comprises a first pattern of transmit signals routed to a plurality of ultrasonic transducers of the ultrasonic sensor. Next, capture 3210 a second set of pixels at the ultrasonic sensor using a second beamforming pattern, wherein the second beamforming pattern comprises a second pattern of ultrasonic transducers, wherein the second beamforming pattern is different than the first beamforming pattern, and wherein pixels of the second set of pixels correspond to positions between pixels of the first set of pixels. Finally, combine 3225 the first set of pixels and the second set of pixels to form the composite image.

In an embodiment, the first beamforming pattern focuses ultrasonic energy above a center 3002 (3102) of each ultrasonic transducer and the second beamforming pattern focuses energy at a corner 3004 (3104) between four (three) adjacent ultrasonic transducers. As an example, two scans per image are taken, with a first scan capturing the first set of pixels and a second scan capturing the second set of pixels. In an embodiment, the first scan is X-Y symmetrical around the center 3002 (3102 of each ultrasonic transducer and the second scan is X-Y symmetrical around the corner 3004 (3104) between the four adjacent ultrasonic transducers.

In another embodiment, after capturing 3210 the second set of pixels, the method 3200 further includes capturing 3215 a third set of pixels at the ultrasonic sensor using a third beamforming pattern. The third beamforming pattern comprises a third pattern of ultrasonic transducers. The third beamforming pattern is different than the first beamforming pattern and the second beamforming pattern. Further, pixels of the third set of pixels correspond to positions either X-Y symmetrical around a target PMUT edge midpoint in one direction or X-Y symmetrical around a target PMUT edge midpoint in an orthogonal direction. For example, the first beamforming pattern focuses ultrasonic energy above a center 3002 of each ultrasonic transducer, the second beamforming pattern focuses energy at a corner 3004 between four adjacent ultrasonic transducers, and the third beamforming pattern focuses energy either at a midpoint 3006 x of an edge between two adjacent ultrasonic transducers or at a midpoint 3006 y of an edge between two adjacent ultrasonic transducers. In this embodiment, the method 3200 concludes with combining 3225 the first set of pixels, the second set of pixels, and the third set of pixels, to form the composite image.

In another embodiment, after capturing 3215 the third set of pixels, the method 3200 further includes capturing 3220 a fourth set of pixels at the ultrasonic sensor using a fourth beamforming pattern. The fourth beamforming pattern comprises a fourth pattern of ultrasonic transducers. The fourth beamforming pattern is different than the first beamforming pattern, the second beamforming pattern, and the third beamforming pattern. Further, pixels of the fourth set of pixels correspond to positions either X-Y symmetrical around a target PMUT edge midpoint in the orthogonal direction or X-Y symmetrical around a target PMUT edge midpoint in the one direction. In other words, pixels of the third set of pixels are X-Y symmetrical around a target PMUT edge midpoint in the X or Y direction and pixels of the fourth set of pixels are X-Y symmetrical around a target PMUT edge midpoint in the Y or X direction. For example, the first beamforming pattern focuses ultrasonic energy above a center 3002 of each ultrasonic transducer, the second beamforming pattern focuses energy at a corner 3004 between four adjacent ultrasonic transducers, the third beamforming pattern focuses energy at a midpoint 3006 x of an edge along the X-axis between two adjacent ultrasonic transducers, and the fourth beamforming pattern focuses energy at a midpoint 3006 y of an edge along the Y-axis between two adjacent ultrasonic transducers, where the Y-axis is orthogonal to the X-axis. In this embodiment, the method 3200 concludes with combining 3225 the first set of pixels, the second set of pixels, the third set of pixels, and the fourth set of pixels to form the composite image.

In some embodiments, more than four sets of pixels may be captured, using the procedures outlined above. In such cases, the beamforming pattern for each set of pixels is different. All sets of captured pixels are then combined 3225 to form the composite image.

In some embodiments, two sets of pixels may be captured 3205, 3210. In other embodiments, three sets of pixels may be captured 3205, 3210, 3215. In yet other embodiments, four sets of pixels may be captured 3205, 3210, 3215, 3220. In all cases, all sets of captured pixels are then combined 3225 to form the composite image.

An electronic device comprises an ultrasonic sensor 1200, a processing logic module 1340, and a processor connected to the processing logic module and configured to perform the steps of generating a composite image having an increased image pixel density in a given density of ultrasonic transducers, as described above.

A method of generating a composite image of a fingerprint uses the method described above. The fingerprint sensing system 1250 comprises a plurality of ultrasonic transducers to transmit a first ultrasonic beam from sets of pixels toward a surface 1216 configured to receive a finger 1252 having the fingerprint thereon and to receive a second ultrasonic beam reflected from the fingerprint. The second ultrasonic generates a signal for processing in a signal processor 1240.

What has been described above includes examples of the subject disclosure. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the subject matter, but it is to be appreciated that many further combinations and permutations of the subject disclosure are possible. Accordingly, the claimed subject matter is intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

In particular and in regard to the various functions performed by the above described components, devices, circuits, systems and the like, the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (e.g., a functional equivalent), even though not structurally equivalent to the disclosed structure, which performs the function in the herein illustrated exemplary aspects of the claimed subject matter.

The aforementioned systems and components have been described with respect to interaction between several components. It can be appreciated that such systems and components can include those components or specified sub-components, some of the specified components or sub-components, and/or additional components, and according to various permutations and combinations of the foregoing. Sub-components can also be implemented as components communicatively coupled to other components rather than included within parent components (hierarchical). Additionally, it should be noted that one or more components may be combined into a single component providing aggregate functionality or divided into several separate sub-components. Any components described herein may also interact with one or more other components not specifically described herein.

In addition, while a particular feature of the subject innovation may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “includes,” “including,” “has,” “contains,” variants thereof, and other similar words are used in either the detailed description or the claims, these terms are intended to be inclusive in a manner similar to the term “comprising” as an open transition word without precluding any additional or other elements.

Thus, the embodiments and examples set forth herein were presented in order to best explain various selected embodiments of the present invention and its particular application and to thereby enable those skilled in the art to make and use embodiments of the invention. However, those skilled in the art will recognize that the foregoing description and examples have been presented for the purposes of illustration and example only. The description as set forth is not intended to be exhaustive or to limit the embodiments of the invention to the precise form disclosed. 

What is claimed is:
 1. A method for generating a composite image having an increased image pixel density by an array of ultrasonic transducers having a given spatial density, the method comprising: capturing a first set of pixels at an ultrasonic sensor using a first beamforming pattern, wherein the first beamforming pattern comprises a first pattern of ultrasonic transducers of the ultrasonic sensor, wherein the first beamforming pattern activates transducers with different signal delays to focus a beam to a single point over a center of an ultrasonic transducer of the array of ultrasonic sensors; capturing a second set of pixels at the ultrasonic sensor using a second beamforming pattern, wherein the second beamforming pattern comprises a second pattern of ultrasonic transducers, wherein the second beamforming pattern is different than the first beamforming pattern, wherein the second beamforming pattern activates different transducers with different signal delays to focus a beam to at least one point over a corner between adjacent ultrasonic transducers of the array of ultrasonic sensors, and wherein pixels of the second set of pixels correspond to positions between pixels of the first set of pixels; and combining the first set of pixels and the second set of pixels to form the composite image.
 2. The method of claim 1, wherein the first beamforming pattern focuses ultrasonic energy above a center of an ultrasonic transducer and wherein the second beamforming pattern focuses energy at a corner between four adjacent ultrasonic transducers.
 3. The method of claim 2, wherein two scans per image are taken, a first scan capturing the first set of pixels and a second scan capturing the second set of pixels.
 4. The method of claim 3, wherein the beamforming pattern of the first scan is X-Y symmetrical around the center of the ultrasonic transducer and the beamforming pattern of the second scan is X-Y symmetrical around the corner between four adjacent ultrasonic transducers.
 5. The method of claim 1, wherein the first beamforming pattern focuses ultrasonic energy above a center of an ultrasonic transducer and wherein the second beamforming pattern focuses energy at a corner between three adjacent ultrasonic transducers.
 6. The method of claim 5, wherein three scans per image are taken, a first scan capturing the first set of pixels, a second scan capturing the second set of pixels, and a third scan capturing a third set of pixels.
 7. The method of claim 6, wherein the beamforming pattern of the first scan is X-Y symmetrical around the center of the ultrasonic transducer and the beamforming pattern of the second scan is X-Y symmetrical around the corner between three adjacent ultrasonic transducers.
 8. The method of claim 1, further comprising: capturing a third set of pixels and a fourth set of pixels at the ultrasonic sensor using a third beamforming pattern and a fourth beamforming pattern, wherein the third beamforming pattern and the fourth beamforming pattern comprise, respectively, a third pattern of ultrasonic transducers and a fourth pattern of ultrasonic transducers, wherein the third beamforming pattern and the fourth beamforming pattern are different than the first beamforming pattern and the second beamforming pattern and from each other, and wherein pixels of the third set of pixels correspond to positions between pixels of the first set of pixels and wherein pixels of the fourth set of pixels correspond to positions between pixels of the first set of pixels different than the pixels of the third set of pixels.
 9. The method of claim 8, wherein the first beamforming pattern focuses ultrasonic energy above a center of the ultrasonic transducer, wherein the second beamforming pattern focuses energy at a corner between four adjacent ultrasonic transducers, wherein the third beamforming pattern focuses energy at a midpoint of an edge along a first axis between two adjacent ultrasonic transducers, and wherein the fourth beamforming pattern focuses energy at a midpoint of an edge along a second axis between two adjacent ultrasonic transducers, wherein the second axis is orthogonal to the first axis.
 10. The method of claim 8, wherein the combining the first set of pixels and the second set of pixels to form the composite image comprises: combining the first set of pixels, the second set of pixels, the third set of pixels, and the fourth set of pixels to form the composite image.
 11. The method of claim 1, wherein the ultrasonic transducers are Piezoelectric Micromachined Ultrasonic Transducer (PMUT) devices.
 12. The method of claim 11, wherein at least one PMUT device comprises: a substrate; an edge support structure connected to the substrate; and a membrane connected to the edge support structure such that a cavity is defined between the membrane and the substrate, the membrane configured to allow movement at ultrasonic frequencies, the membrane comprising: a piezoelectric layer, first and second electrodes coupled to opposing sides of the piezoelectric layer, and a mechanical support layer connected to the first electrode.
 13. The method of claim 12, wherein the at least one PMUT device further comprises an interior support structure disposed within the cavity and connected to the substrate and the membrane.
 14. An electronic device comprising: an ultrasonic sensor; a processing logic module; and a processor connected to the processing logic module and configured to perform the steps of generating a composite image having an increased image pixel density by an array of ultrasonic transducers having a given spatial density by: capturing a first set of pixels at an ultrasonic sensor using a first beamforming pattern, wherein the first beamforming pattern comprises a first pattern of ultrasonic transducers of the ultrasonic sensor, wherein the first beamforming pattern activates transducers with different signal delays to focus a beam to a single point over a center of an ultrasonic transducer of the array of ultrasonic sensors; capturing a second set of pixels at the ultrasonic sensor using a second beamforming pattern, wherein the second beamforming pattern comprises a second pattern of ultrasonic transducers, wherein the second beamforming pattern is different than the first beamforming pattern, wherein the second beamforming pattern activates different transducers with different signal delays to focus a beam to at least one point over a corner between adjacent ultrasonic transducers of the array of ultrasonic sensors, and wherein pixels of the second set of pixels correspond to positions between pixels of the first set of pixels; and combining the first set of pixels and the second set of pixels to form the composite image.
 15. The electronic device of claim 14, wherein the ultrasonic transducers are Piezoelectric Micromachined Ultrasonic Transducer (PMUT) devices.
 16. The electronic device of claim 15, wherein at least one PMUT device comprises: a substrate; an edge support structure connected to the substrate; and a membrane connected to the edge support structure such that a cavity is defined between the membrane and the substrate, the membrane configured to allow movement at ultrasonic frequencies, the membrane comprising: a piezoelectric layer, first and second electrodes coupled to opposing sides of the piezoelectric layer, and a mechanical support layer connected to the first electrode.
 17. The electronic device of claim 16, wherein the at least one PMUT device further comprises an interior support structure disposed within the cavity and connected to the substrate and the membrane.
 18. A method of generating a composite image of a fingerprint with a fingerprint sensor comprising an ultrasonic sensor comprising a plurality of ultrasonic transducers to transmit a first ultrasonic beam from sets of ultrasonic transducers toward a surface configured to receive a finger having the fingerprint thereon and to receive a second ultrasonic beam reflected from the fingerprint, the second ultrasonic beam to generate a signal for processing in a signal processor, the method comprising generating an image having an increased image pixel density by an array of ultrasonic transducers having a given spatial density, the method comprising: capturing a first set of pixels at the ultrasonic sensor using a first beamforming pattern, wherein the first beamforming pattern comprises a first pattern of ultrasonic transducers of the ultrasonic sensor, wherein the first beamforming pattern activates transducers with different signal delays to focus a beam to a single point over a center of an ultrasonic transducer of the array of ultrasonic sensors; capturing a second set of pixels at the ultrasonic sensor using a second beamforming pattern, wherein the second beamforming pattern comprises a second pattern of ultrasonic transducers, wherein the second beamforming pattern is different than the first beamforming pattern, wherein the second beamforming pattern activates different transducers with different signal delays to focus a beam to at least one point over a corner between adjacent ultrasonic transducers of the array of ultrasonic sensors, and wherein pixels of the second set of pixels correspond to positions between pixels of the first set of pixels; and combining the first set of pixels and the second set of pixels to form the image.
 19. The method of claim 18, wherein the first beamforming pattern focuses ultrasonic energy above a center of an ultrasonic transducer and wherein the second beamforming pattern focuses energy at a corner between four adjacent ultrasonic transducers.
 20. The method of claim 19, wherein two scans per image are taken, a first scan capturing the first set of pixels and a second scan capturing the second set of pixels.
 21. The method of claim 20, wherein the beamforming pattern of the first scan is X-Y symmetrical around the center of the ultrasonic transducer and the beamforming pattern of the second scan is X-Y symmetrical around the corner between four adjacent ultrasonic transducers.
 22. The method of claim 18, wherein the first beamforming pattern focuses ultrasonic energy above a center of an ultrasonic transducer and wherein the second beamforming pattern focuses energy at a corner between three adjacent ultrasonic transducers.
 23. The method of claim 22, wherein three scans per image are taken, a first scan capturing the first set of pixels, a second scan capturing the second set of pixels, and a third scan capturing a third set of pixels.
 24. The method of claim 23, wherein the beamforming pattern of the first scan is X-Y symmetrical around the center of the ultrasonic transducer and the beamforming pattern of the second scan is X-Y symmetrical around the corner between three adjacent ultrasonic transducers.
 25. The method of claim 18, further comprising: capturing a third set of pixels and a fourth set of pixels at the ultrasonic sensor using a third beamforming pattern and a fourth beamforming pattern, wherein the third beamforming patter comprises a third pattern of ultrasonic transducers and the fourth beamforming pattern comprises a fourth pattern of ultrasonic transducers, wherein the third beamforming pattern and the fourth beamforming pattern are different than the first beamforming pattern and the second beamforming pattern and from each other, and wherein pixels of the third set of pixels correspond to positions between pixels of the first set of pixels and wherein pixels of the fourth set of pixels correspond to positions between pixels of the first set of pixels different than the pixels of the third set of pixels.
 26. The method of claim 25, wherein the first beamforming pattern focuses ultrasonic energy above a center of the ultrasonic transducer, wherein the second beamforming pattern focuses energy at a corner between four adjacent ultrasonic transducers, wherein the third beamforming pattern focuses energy at a midpoint of an edge along a first axis between two adjacent ultrasonic transducers, and wherein the fourth beamforming pattern focuses energy at a midpoint of an edge along a second axis between two adjacent ultrasonic transducers, wherein the second axis is orthogonal to the first axis.
 27. The method of claim 25, wherein the combining the first set of pixels and the second set of pixels to form the composite image comprises: combining the first set of pixels, the second set of pixels, the third set of pixels, and the fourth set of pixels to form the composite image.
 28. The method of claim 22, wherein the ultrasonic transducers are Piezoelectric Micromachined Ultrasonic Transducer (PMUT) devices.
 29. The method of claim 28, wherein at least one PMUT device comprises: a substrate; an edge support structure connected to the substrate; and a membrane connected to the edge support structure such that a cavity is defined between the membrane and the substrate, the membrane configured to allow movement at ultrasonic frequencies, the membrane comprising: a piezoelectric layer, first and second electrodes coupled to opposing sides of the piezoelectric layer, and a mechanical support layer connected to the first electrode.
 30. The method of claim 29, wherein the at least one PMUT device further comprises an interior support structure disposed within the cavity and connected to the substrate and the membrane. 